The present invention generally relates to metallurgical furnaces and, more particularly, to improvements in the design and construction of elongated, internally cooled support rails commonly employed in walking beam and so-called pusher-type furnaces.
The function of such rails is to support and to provide for the continuous transport of workpieces, such as ingots, slabs, rods, bars or like heavy metallic workpieces through a heating chamber. The so-called pusher-type furnaces push the workpieces along the elongated support rails and heat the workpieces on all sides thereof.
In such furnaces, the rails are cooled, usually by circulating cooling fluid through interior passages of the rails, so that the rails will not themselves be deformed at the elevated temperatures of the furnace. Thus, direct contact between the workpieces and the rails must be avoided since otherwise undesirable undercooled zones or darkened areas in the region of the workpiece surface which contacts the support will be formed due to the difference in temperature. These undercooled zones are very undesirable because they adversely affect material characteristics, particularly during subsequent rolling.
In order to eliminate the formation of such undercooled zones and to protect the rail from excessive wear, so-called wear-resistant strips, or "riders," or workpiece-engaging elements constituted of heat-insulating material are mounted on the upper side of the rails over the entire length thereof. The workpieces are supported from below on these riders for the purpose of preventing undercooling of those underside portions of the workpieces which would otherwise be in direct contact with the internally-cooled rails.
In addition, in order to insulate the lateral sides and bottom side of the rail, a jacket constituted also of heat-insulating material, such as ceramic material, is placed about the rail.
It is desirable in the construction of metallic furnaces for those skilled in the art to keep the number of support rails as low as possible so that undesirable heat losses can be prevented. Also, the support rails exhibit the further disadvantage that they tend to screen and hinder the flow of heat energy being directed towards the underside of the workpiece because of their very presence. For the same reasons, it is also desirable to keep the spacing between adjacent pairs of rails as large as possible, although this requirement must be counterbalanced by the size of the smallest workpiece which is expected to be advanced through the furnace and, in addition, by the fact that if the rails are located too close to each other, not enough heat will arrive at the underside of the workpiece located between the rails.
Furthermore, in determining the appropriate spacing between the rails, one must keep in mind that the workpieces undergo not only motion in the direction of the elongation of the rail but are also subject to a certain amount of lateral displacement transversely of the rail.
The above considerations dictate, for practical operation, that the length of the workpieces by only very slightly longer than the spacing between the rails. However, such prior art constructions have not proven altogether satisfactory since, in the event that a workpiece slides off the workpiece-engaging elements as a result of inadvertent or careless handling, the workpiece first falls on the ceramic jacket and fractures the same and thereupon falls to the furnace floor.
As a result, the rails are no longer heat-insulated and, in a furnace which operates at elevated temperatures for heat-treating of steel workpieces, the heat loss to the exposed rails and the consumption of cooling fluid per unit surface area and time is increased almost by a factor of 10 times. Even if, for example, only one-tenth of the ceramic jacket is chipped away, the heat loss and consumption of cooling fluid is increased up to two times.